This invention relates to the manufacture of data storage disks. In particular, the present invention is a method of manufacturing a stamper assembly and a stamper assembly for producing replica optical data storage disks that minimizes stamper wear and minimizes defects in the molded replica disks that would adversely affect the readability of the manufactured disks.
Optical data storage disks have gained widespread acceptance for the storage, distribution and retrieval of large volumes of information. These disks include audio and video program material, as well as computer programs and data. Formats of optical data storage disks include audio CD (compact disc), CD-R (CD-recordable), CD-ROM (CD-read only memory), DVD (digital versatile disk or digital video disk) media, DVD-RAM (random access memory), and various types of rewritable media, such as magneto-optical (MO) disks and phase change optical disks.
In general, optical disks (such as CD-ROM""s) are produced using a disk replication process. A master disk is made having a desired surface relief pattern formed therein which represents the data to be replicated. The surface relief pattern is typically created using an exposure step (e.g., by laser recording). The master disk is used to make a stamper, which, in turn, is used in an injection molding process to make production quantities of replica optical disks. As such, the surface relief pattern and precision of the single master disk can be transferred into many inexpensive replica disks, such that each replica disk contains the data and tracking information which was encoded in the master disk.
The optical disk replication process typically entails the use of a mold assembly that generally includes a fixed side and a moving side. To form a replica optical disk formatted on only one side (i.e., typically termed a single-sided disk), the stamper is attached to the moving side of the mold assembly for duplicating a desired surface relief pattern (i.e., lands, grooves and/or pits) into a replica disk substrate. Typically, the stamper is removably secured to a mirror block of the moving side of the mold assembly via an inner holder and an outer holder. The inner holder engages an inner peripheral edge of a central opening of the stamper, while the outer holder engages an outer peripheral edge of the stamper. The inner and outer holders are removable to permit changeout of the stamper, which allows the mold assembly to be used to manufacture replica disk substrates having different surface relief patterns. In addition, the ability to changeout the stamper also allows damaged or worn stampers to be replaced with a new stamper having the same surface relief pattern as the stamper that is being replaced. A central area of the mold assembly generally includes several tooling parts, such as a movable gate cut for cutting a central opening in the replica disk substrates.
During the disk molding process, a resin, typically optical grade polycarbonate, is forced into a substrate cavity within the mold assembly through a sprue channel to form the disk substrate. The surface relief pattern (i.e., the formatted surface) defining the information side of the optical disk is replicated in the disk substrate by the stamper as the substrate cavity is filled. After filling, the gate cut is brought forward to cut a center hole in the disk substrate. After the replica disk substrate has sufficiently cooled, the mold assembly is opened and the gate cut and a product eject may be brought forward for ejecting the formatted replica disk substrate off of the stamper. Typically, the information side of the replica disk substrate is then coated with a reflectance layer, such as a thin layer of aluminum, and in the case where the replica disk substrate is a CD, the reflectance layer is followed by a protective layer of lacquer to complete the process for producing single-sided replica, optical data storage disks. Since the fixed side of the above described mold assembly cannot accommodate a stamper, to produce a replica optical disk formatted on both sides (i.e., typically termed a double-sided disk), requires that two single-sided disks be secured together in a back-to-back relationship such their formatted surfaces (i.e., the surfaces having the relief pattern of the master disk) face outward.
Although the above described mold assembly and replication process produces adequate replica, optical data storage disks, there are some disadvantages. For example, since the inner and outer holders of the mold assembly only secure the stamper to the mirror block at the inner and outer peripheral edges of the stamper, the stamper can move relative to the mirror block. This movement is caused by pressure and temperature cycling (i.e., expansion and contraction) of the stamper during the molding process, and stamper flexing during opening of the mold assembly and the subsequent ejection of the formatted replica disk substrate off of the stamper. The relative movement between the stamper and the mirror block causes wear on the backside of the stamper as well as wear to the mirror block. Any excessive wear to either of these components would adversely affect the playability of the manufactured, replica optical disks. For instance, excessive wear of the stamper and/or the mirror block causes roughness to be molded into the replica disk substrates. This roughness increases the noise floor causing playability issues with the molded optical disk. In extreme cases, this relative movement between the stamper and the mirror block can result in catastrophic damage to one or both of these components, requiring immediate replacement of the damaged element. Because the stamper can become worn or damaged over time, the typical stamper has an average useful lifetime spanning the production of only approximately 50,000 replica disk substrates.
The above described mold assembly and replication process has further disadvantages. For example, because the stamper flexes during opening of the mold assembly and the subsequent ejection of the formatted replica disk substrate, the stamper loses contact with the mirror block. Since the mirror block acts as a heat sink to cool the stamper during the replication process, this loss of contact between the stamper and the mirror block causes the transfer of heat from the stamper to the mirror block to be nonuniform. This nonuniform heat transfer results in uneven cooling of the replica disk substrate, which can affect the formation of the surface relief pattern and ultimately, adversely affect the playability of the manufactured, replica optical disk. In severe cases, this nonuniform heat transfer can cause the replica disk substrates to prematurely separate from the stamper resulting in incomplete formation of the surface relief patterns and unusable replica optical disks.
There is a need for an improved stamper assembly for use in a mold assembly to produce replica optical data storage disks, and for an improved method of stamper assembly manufacture. In particular, there is a need for a stamper assembly that minimizes stamper wear, and thereby, minimizes defects in the molded replica disks that would adversely affect the playability of the manufactured disks. The stamper assembly should increase the average useful lifespan of a stamper to allow more replica optical disks to be produced from each stamper assembly. In addition, the stamper assembly should permit even cooling of the formed replica disk substrates to further minimize defects that can affect playability. Moreover, the stamper assembly should provide these features while being relatively easy and inexpensive to manufacture.
The present invention is a stamper assembly for forming an optical data storage disk in a disk molding process. The stamper assembly includes a block element having a first major surface, and a stamper member having a first major surface and an opposite, second major surface. The first major surface of the stamper member is adapted to contact a disk molding material for forming an optical data storage disk in a disk molding process. The stamper assembly further includes a medium for securing the stamper member to the block element, such that substantially the entire second major surface of the stamper member is affixed to the first major surface of the block element. This arrangement prevents relative movement between the stamper member and the block element. The stamper assembly is useable in a mold assembly either by itself or with another like stamper assembly to form either single-sided or double-sided optical data storage disks.
The stamper assembly of the present invention is manufactured by first applying a curable liquid material to substantially the entire first major surface of the block element. A forming stamper is then positioned on the curable liquid material such that substantially an entire first major surface of the forming stamper contacts the liquid material. Next, the liquid material is cured to form a substantially rigid cured layer on the block element. Once cured, this cured layer of once liquid material is affixed to substantially the entire first major surface of the block element so as to prevent relative movement between the cured layer and the block element. The forming stamper is then removed from the cured layer leaving the stamper assembly wherein the cured layer defines the stamper member for forming optical disks in a disk molding process. In an alternative embodiment of the stamper assembly, the stamper member is made of metal and is secured to the block element via an adhesive.
This stamper assembly prevents relative movement between the stamper member and the block element, since substantially the entire second major surface of the stamper member is affixed to the first major surface of the block element. Because the stamper member is totally secured to the block element, movement of the stamper member relative to the block element due to pressure and temperature cycling (i.e., expansion and contraction) during the molding process is virtually eliminated. In addition, stamper flexing during opening of the mold assembly and the subsequent ejection of the formatted replica disk substrate off of the stamper member is essentially nonexistent. Since the stamper member no longer loses contact with the block element, the block element uniformly draws heat from the stamper member to provide even cooling of the replica disk substrates. Even cooling of the disk substrates improves the formation of the surface relief patterns and ultimately the playability of the manufactured replica optical disks. Moreover, the medium for securing the stamper member to the block element provides insulating properties that slow the transfer of heat from the stamper member to the block element. This slowing of heat transfer allows the replica disk substrates to remain hotter slightly longer during the molding process, which makes the surface relief pattern easier to form.
With virtually no relative movement between the stamper member and the block element, excessive wear on the second major surface (i.e., backside) of the stamper member and excessive wear to the block element is substantially eliminated. Hence, the noise floor increase and the playability issues, due to roughness in the molded replica optical disks because of excessive wear to either of these components, is no longer a principal concern. Moreover, because stamper member wear has been substantially curtailed, the stamper assembly of the present invention has an increased average, useful production lifetime. In addition, since the stamper member is directly affixed to the first major surface of the block element, the stamper assembly of the present invention is useable either by itself or with another like stamper assembly on either one or both of the fixed and moving sides of the mold assembly to form either single-sided or double-sided optical data storage disks. Lastly, the stamper assembly of the present invention provides all these features while being relatively easy and inexpensive to manufacture.